Merthyr Tydfil, South Wales Valleys
Semi-detached rear extension in Merthyr Tydfil
We plan and build rear extensions for semi-detached houses for homeowners in Merthyr Tydfil. Single or two-storey extensions for semi-detached houses, with side access and one party wall. Start with a free site visit, then a written price once the design is agreed.
Merthyr Tydfil and its postcode districts CF47 and CF48 are part of our South Wales Valleys coverage. In Merthyr Tydfil we measure the attached neighbour's extension at the survey, because it often sets the sensible depth for yours.
Book a free site visit
Tell us about the house and we'll call to arrange a free, no-obligation visit.
How much does a semi-detached rear extension cost in Merthyr Tydfil?
For Merthyr Tydfil we work from the Wales rate: £1,770–£2,880 per square metre of new floor, including VAT, standard specification. Prices in Wales sit below our West Midlands baseline; sloping sites are the main variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £21,000–£34,500 |
| 4 m wide × 5 m deep (20 m²) | £35,500–£57,500 |
| 4 m wide × 6 m deep (24 m²) | £42,500–£69,000 |
Your written price follows a measured survey and an agreed design, so it reflects your house, not an average.
Do you need planning permission for a semi-detached rear extension in Merthyr Tydfil?
Here is how the rules in Wales apply to a semi-detached rear extension in Merthyr Tydfil.
Welsh permitted development allows a single-storey rear extension of up to 4 metres in depth and 4 metres in height, subject to boundary and garden-coverage limits. There is no larger-extension prior approval scheme in Wales.
In Wales a rear extension of more than one storey can be permitted development if the ground floor projects no more than 4 metres and the upper floor no more than 3 metres, with at least 10.5 metres to the rear boundary. It is not permitted development in conservation areas, National Parks or National Landscapes, so many double-storey schemes need a householder application.
Conservation areas, National Parks and National Landscapes restrict permitted development in Wales, and listed buildings need listed building consent. We check your house's planning history and any conservation area before drawing, so the route is clear before you spend on plans.
What are homes in Merthyr Tydfil like to extend?
Stone terraces along the valley floors and post-war semis higher up are typical of Merthyr Tydfil. Sloping sites are common, so floor levels and retaining walls are designed at the start.
How a semi-detached rear extension in Merthyr Tydfil comes together
Survey visit
We visit free of charge, measure up, check access, drainage and neighbours' extensions, and note what you want the room to do.
Drawings and budget
Floor plans and elevations for the options, each with a guide price.
Planning and regulations
We take the design through the right planning route, then produce the construction drawings and engineer's calculations for building control.
Build and sign-off
We build to the approved drawings with regular updates, then hand over the building control completion certificate and any guarantees from suppliers.
Semi-detached rear extensions near Merthyr Tydfil
Neighbouring places we cover include Aberdare (3.8 miles) and Mountain Ash (4.4 miles).
- Semi-detached rear extension in Aberdare
- Semi-detached rear extension in Mountain Ash
- Semi-detached rear extension in Tredegar
- Semi-detached rear extension in Treharris
- Semi-detached rear extension in Rhondda
Other work in Merthyr Tydfil:
FAQ
Semi-detached rear extension questions in Merthyr Tydfil
How long does a rear extension take to build in Merthyr Tydfil?
Most single-storey rear extensions take 10 to 16 weeks on site and two-storey extensions 16 to 26 weeks, after design and approvals.
What postcode areas do you cover around Merthyr Tydfil?
Including CF47 and CF48, and the surrounding South Wales Valleys area.
What if my neighbour has already extended?
That can make a matching depth easier to justify. We measure theirs at the survey.
Do I need a party wall agreement?
In Wales, usually yes if the extension is on or near a shared boundary or close to a neighbour's foundations. We serve the notices.
Will I need a structural engineer?
Yes for the beam over the new opening and usually the foundations; we arrange them and their calculations go to building control.
Who will build my extension?
Vetted building teams working under contract to us. Your contract is with S&K Property Investments and Improvement Ltd for the design and the build.